How to get mouse displacement over last frame?

I noticed that there was a function, some time ago, the name of which i forgot, that i could use to get the mouse displacement. I'm using SFML and the approach i am using on windows to calculate the mouse displacement does not work on mac: i reset the mouse to the center of the screen everytime i calculate the displacement but on my mac the object animated by the displacement does not move in a fluid manner. So i am wondering if the mouse displacement can be queried automatically in some way so i would not use my current approach.